1. Field of the Invention
The present invention relates to a signal reproducing apparatus for reproducing information signals recorded in oblique tracks on a magnetic tape by means of a magnetic head.
2. Description of the Prior Art
In a signal reproducing apparatus for reproducing information signals recorded as oblique tracks on a tape, the tape is normally helically scanned by a rotary head. Also, the signals recorded on a tape are divided in each track for convenience during reproduction.
Tracking control of the rotary head and the oblique tracks on the tape was hitherto effected by reproducing the control signal recorded by a fixed magnetic head at one side in the widthwise direction of the tape by the same fixed head, and adjusting the reproduced control signal and the rotation phase of the rotary head in a specific phase relation. This method is employed, for example, in the videotape recorder (VTR) of the VHS format.
In this method, however, a fixed magnetic head is required for tracking control. Provision of such a fixed magnetic head brings about a problem with regard to its mounting position where downsizing the magnetic recording and reproducing apparatus is desired. There is proposed, accordingly, a method of automatic track finding (ATF) for controlling tracking of the rotary head by using only the reproduction output of the rotary head for reproduction without using a fixed head, which is employed, for example, in an 8 mm VTR. The ATF system is effective not only for downsizing and simplifying the mechanism, but also for automating the tracking adjustment and narrowing the tracks. The ATF system is expected to be employed in more and more apparatuses for tracking control henceforth.
In tracking control, it is important to enhance the response speed. It is a particularly important subject for the controllability of the VTR to shorten the required time (tracking lead-in time) from the stopped state of the tape until tracking is completed to become a stable state. This is because the tracking lead-in time occupies a large portion in the total time from the stopped state of the tape until the picture is reproduced or the splicing is started. Here, the term "splicing" denotes a continuation of recording from an end of a specific already recorded area. In particular, when splicing, if the operator presses the record button at a desired position, it takes a long time for the tape running to become stabilized. As a result, it is impossible to record at the desired moment, and a portion of the desired recording is not recorded.
Several methods have been proposed for shortening the tracking lead-in time. According to a certain method, for example, the moving distance from a specific position is detected and recorded when stopping, and the starting timing to the reference signal is adjusted depending on this distance.
In another example of using a control signal which is detected by a fixed head, as disclosed in Japanese Laid-open Patent 1-149266, in order to shorten the tracking lead-in time, always maintaining constant the relative position of the head and track recorded on the tape when stopping, the tape running start timing is synchronized with the head changeover signal so that the head may trace the track center in the starting transient and stationary state. In this example, by running the tape at low speed without phase control, the tape is stopped in a specified time after detecting the pulse of the control signal. As a result, the relative position of the head and the track is kept constant. This method of controlling the stopping position is applicable, in principle, also to the ATF system.
In the foregoing example, however, when stopping, it is necessary to execute a preparatory step of detecting and storing the running distance from a specific position, or stopping at a specific position precisely. In such stopping actions, a problem arises in that there are many elements influenced by fluctuations of the mechanism, that is, many uncertain elements. If the preparatory action cannot be effected right after the tape loading action, such rapid tracking lead,in is impossible. Without rapid tracking lead-in, the required time from the stopped state till the appearance of a picture or the start of splicing is extended, and incomplete recording occurs, particularly during splicing.